Incandescent lamps have many uses in the field of earthmoving or construction equipment. For example, they may be used to provide illumination, to enable the operator to drive a vehicle or to operate a work implement. Another use of incandescent lamps in the earthmoving and construction industries is to provide visual indications of the status of a vehicle or operation.
For example, in U.S. Pat. No. 4,845,975 issued to Christos T. Kyrtsos et al on Jul. 11, 1989, a pair of incandescent lamps provide an indication of the loading condition of an off-highway truck relative to rated capacity. The lamps are placed such that they are viewable by the operator of the loading vehicle, e.g., a wheel loader.
These lamps are mounted on the off-highway truck and must be large enough to be readily seen by the operator of the loading vehicle. Large lamps require large driving currents. Because of the requirement for large currents, the driver circuits for the lamps must consist of large current capacity components, making the driver circuits bulky and expensive.
Additionally, the driver circuits must be protected from external faults, e.g., faults to battery, open circuits, and faults to ground. It is also desirable to detect such faults. Typically such protection and detection is accomplished by additional circuitry. The additional circuitry detects certain conditions of the driver circuit and shuts the driver off or isolates the driver circuit. The additional circuitry also adds to the size and expense of the driver circuit.
The present invention is directed at solving one or more of the problems as set forth above.